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```Introduction to Electronics: The Relay

Make] Projects

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Introduction to Electronics: The

Relay

Written By: KRA5H

TOOLS:

PARTS:

Snap Circuits Extreme 750 set (1)

Battery Holder (2-AA) # 6SC B1 (1)
Base Grid (11" x IT) # 6SC BG (1)
Press Switch #6SCS2(1)
RedLED#6SCD1 (1)
Relay #6SC S3 (1)
Conductor with 2-snaps # 6SC 02 (3)
Conductor with 3-snaps # 6SC 03 (1)
Conductor with 4-snaps # 6SC 04 (1)

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Page 1 of 8

Introduction to Electronics: The Relay

Step 1 — Introduction to Electronics: The Relay

• What's a relay? You've probably
seen a relay race where one runner
hands off a baton to another
runner. Similarly, an electronic
relay hands off control from one
circuit to another.

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Page 2 of 8

Introduction to Electronics:

: The Relay

Step 2

© Make Projects www.makeprojects.com Page 3 of 8

Introduction to Electronics: The Relay

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Figure 1: Relay off

Figure 2: Relay on

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• A relay is a very simple device
consisting of an electromagnet, an
armature (a switch that closes
when attracted by the
electromagnet), and a spring that is
connected to the armature. You
can see in the diagrams (Source:
How Stuff Works) how the relay
works.

• In Figure 1 of the diagram, there
are two circuits. The first circuit is
a battery (3 volts), a switch and an
electromagnet. The second circuit
is a battery (6 volts), a light bulb
and the relay's armature. While the
switch to the electromagnet is off,
no current can flow from the 3 volt
battery through the electromagnet.
So, the armature-switch is off and
no current can flow from the 6 volt
battery to power the lamp in the
second circuit.

• In Figure 2 the switch to the
electromagnet circuit is switched
on. When current from the 3 volt
battery flows through the
electromagnet, the electromagnet
creates a magnetic field that
attracts the armature to close the
circuit to the lamp. Now current
can flow from the 6 volt battery to
the lamp, and the lamp lights up.

• If you look closely at Figure 2,
you'll notice that while the
armature-switch is closed allowing
the current in the lamp circuit to

Page 4 of 8

Introduction to Electronics: The Relay

flow from the 6 volt battery to the
lamp, it does not come into contact
with the electromagnet.

This means that the 6 volts from
the lamp circuit cannot flow into the
electromagnet circuit. Thus, the 3
volts in the electromagnet circuit
and the 6 volts in the lamp circuit
remain separate.

Step 3

• This is the electronic schematic
diagram of a relay. The curly line
represents the electromagnetic coil
and the vertical lines represent the
metal core the coil is wrapped
around. The switch at the top of the
diagram represents the armature.

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Page 5 of 8

Introduction to Electronics

The Relay

Step 4

• This is the electronic schematic of
the circuits from figures 1 and 2
above.

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Page 6 of 8

Introduction to Electronics: The Relay

Step 5

• Build the circuit demonstrated in the photographs.

• When you press the Press Switch (S1) you will hear the relay click as current passes from
the 3 volt battery block (B1) through the electromagnet. The electromagnet creates a
magnetic field that attracts the metal armature.

• When you release the Press Switch you will hear the relay click again since the current
has been cut from the electromagnet. This causes the electromagnetic field to collapse so
the armature is no longer attracted by the electromagnet and the spring attached to the
armature returns the armature to its rest position.

• Often when using electronic relays in circuits it is recommended that you insert a flyback
diode to protect sensitive electronics. The magnetic coil in the relay stores electricity like
a capacitor and when the voltage is cut from the coil the current can flow back into the
circuit in a way that is undesirable.

• I've included the red LED to demonstrate this phenomenon and you can review this video
to watch the LED flash when I release the Press Switch (S2).

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Page 7 of 8

Introduction to Electronics

The Relay

Step 6

• The following are a couple of
videos that demonstrate the use of
the relay in simple circuits:

• This first video is a very simple
circuit that launches a flying
disc.

• The second video demonstrates
using the relay in a laser tripwire
circuit to sound an alarm.

• For a complete step-by-step build
of the laser tripwire and alarm
Laser Tripwire and Alarm Using
Snap Circuits

Relay diagram source: http://electronics.howstuffworks.com/rel.

This document was last generated on 201 2-1 0-30 07:1 8:40 PM.